The invention relates generally to mixers and cavitation devices that are utilized for processing heterogeneous and homogeneous fluids through the controlled formation of cavitation bubbles that serve as independent chemical mini-reactors, and uses the energy released upon implosions of these cavities to alter quickly said fluids. The device may find applications in petroleum, chemical, pharmaceutical, fuel, food and other industries to prepare solutions, emulsions, and dispersions and to improve mass and heat transfer processes.
More particularly, the invention relates to modifying complex fluids composed of a number of different compounds and utilizes cavity implosion energy to improve said fluids' homogeny, viscosity, and/or other physical characteristics, alter their chemical composition by converting compounds, and obtain upgraded, more valuable products.
It has been reported that the elevated pressure, increased temperature and vigorous mixing supplied by either acoustic and/or hydrodynamic cavitations both initiate and accelerate numerous reactions and processes. Enhancing the reactions and processes by means of the energy released upon the collapse of the cavities in the flow has found application in a number of technologies that are used for upgrading, mixing and pumping, and expedition of chemical conversions. While extreme pressure or tremendous heat can be detrimental, the outcome of controlled processing is beneficial.
Cavitation can be of different origins, such as hydrodynamic, acoustic, laser-induced or generated by the direct injection of steam into a sub-cooled fluid, which produces collapse conditions similar to those of hydrodynamic and acoustic cavitations (Young, 1999; Gogate, 2008; Mahulkar et al., 2008). Direct steam injection cavitation coupled with acoustic cavitation exhibits up to 16 time's greater efficiency, as compared to acoustic cavitation alone.
Hydrodynamic cavitation is the phenomenon of the formation of vapor cavities in fluid flow, which is followed by bubble collapse in a higher-pressure zone. In practice, the process is carried out as follows. The fluid is fed in the device's inlet passage. In a localized zone, the flow accelerates causing its pressure to drop (Bernoulli's principle). This results in the formation of bubbles composed of the vapors of compounds that boil at given condition. When the bubbles move beyond the boundary of the localized zone, the pressure in the flow increases, and the bubbles collapse, exposing the vapors found within to a high pressure and temperature, shearing forces, shock waves, acoustic vibration and/or electromagnetic irradiation. Each cavitation bubble serves as an independent mini-reactor, in which chemical and physical alterations are taking place. The pressure and temperature are significantly higher than in many industrial processes. The further alteration of fluid composition results from chemical reactions taking place in adjacent layers of fluid.
When the fluid's temperature approaches its boiling point, the formation of bubbles is noticeable. If fluid is pressured in a hydrodynamic cavitator at a suitable velocity, as a result of the decreased hydrostatic pressure (Bernoulli's principle), the cavitation bubbles will form at a concentration of hundreds in 1 mL. Their formation can be avoided by an increase in pressure. Small particulate and impurities serve as nuclei for the cavitation bubbles, which may reach several millimeters in the diameters, depending on the conditions. The bubbles take up space normally occupied by fluid, resisting to the flow and increasing the pressure. If the cavities relocate in a slow-velocity, high-pressure zone (reversed Bernoulli's principle), they will implode within a short time of 10−8-10−6 s. The implosion is accompanied by drastic jump in both pressure and temperature, up to 1,000 atm and 5,000° C., correspondingly, and results in the formation of the local jet streams with the velocities of 100-m/s and higher (Suslick, 1989; Didenko et al., 1999; Suslick et al., 1999; Young, 1999). The main disadvantage of an excessively high pressure is excessive heat release, which may become a problem if overheating is detrimental to the products' quality and safety. The collapse of cavities is accompanied by generation of shock waves, vigorous shearing forces, and heating, and releases a significant amount of energy, which activates atoms, molecules and radicals located within the gas-phase bubbles and the atoms, molecules and radicals within the surrounding fluid, and initiates chemical reactions and processes and/or dissipates into the surrounding (Sharma et al., 2008; Kalva et al., 2009). In many cases, the cavity implosion is light emission-free. Often, it is accompanied by emission of ultraviolet and/or visible light, which may induce photochemical reactions and generate radicals (Zhang et al., 2008).
The cavitation phenomenon is categorized by the dimensionless cavitation number Cv, which is defined as: Cv=(P−Pv)/0.5 ρV2, where P is the recovered pressure downstream of the constriction, Pv is the vapor pressure of fluid, V is an average velocity of fluid at the orifice, and ρ is its density. The cavitation number, at which the cavitation starts, is cavitation inception number Cvi. Cavitation ideally begins at Cvi=1, and the Cv<1 implies a high degree of cavitation (Gogate, 2008; Passandideh-Fard and Roohi, 2008). The effect of surface tension and size of cavities on the hydrostatic pressure is defined as follows: Pi=P0+2a/R, where Pi is the hydrostatic pressure, a is the surface tension, and R is the radius of the bubble. The smaller the bubble, the greater the energy released during its implosion. Another important term is the processing ratio, which is a number of cavitation events in a unit of flow.
The cavitation is more dramatic in viscous fluids. For example, if crude oil flow moves at a proper speed causing its pressure to reach the vapor pressure of some hydrocarbon(s) constituents, cavitation will occur. The cavitation separates the liquid-phase high-boiling-point compounds and their particles suspended in liquid compounds from the entrapped gases, water steam and vapors of the affected compounds.
Processing fluids with cavitation generated by the sound waves lying in either acoustic (frequency is 20 Hz-20 KHz) or ultrasound (frequency>20 KHz) ranges does not offer an optimized method. Disadvantage of the processing is its batch environment. In many cases, the technology could not be applied efficiently in a continuous process, because the energy density and the residence time would be insufficient for the high throughput. For instance, the intensity threshold of ultrasound cavitation in water exceeds 0.3 W/cm2. The sound cavitation technology suffers from other drawbacks. Since the effect diminishes with increase in a distance from the radiation source, the treatment efficacy depends on a container size and is low with large vessels. In addition, alterations in the fluid under treatment are not even and take place at the specific locations, depending on the radiation frequency of the source. Thus, the efficacy of the sound treatment further decreases.
The hydrodynamic cavitation device does not require using any vessel, as do the sound or ultrasound-induced cavitations. At the present time, numerous flow-through hydrodynamic cavitation devices are known. See, for example, the U.S. Pat. No. 6,705,396 to Ivannikov et al. and the U.S. Pat. Nos. 7,207,712, 6,502,979 and 5,971,601 to Kozyuk that describe different hydrodynamic cavitation systems and their practical usage.
U.S. Pat. No. 7,338,551 to Kozyuk discloses device and method for generating bubbles in liquid that passes through a first local constriction of the hydrodynamic cavitation device at a velocity of at least 12 m/s and then is mixed with gas to affect implosion within the second cavitation field. Although this device provides two zones of the cavitation, its efficiency may become unsatisfactory when the higher number of the consecutive cavitations is desired.
Another approach illustrated in the U.S. Pat. No. 5,969,207 to Kozyuk uses a flow-through passage accommodating a baffle body that generates a hydrodynamic cavitation with the degree of cavitation of at least 1 to initiate chemical reactions and change qualitative and quantitative composition of liquid hydrocarbons.
The patent of Russia No. 2158627, B 01 J 5/08 introduces the cavitation mixer comprising a cylindrical working chamber, a nozzle shaped as a convergent cone for fluid feeding and a cone nozzle for discharging the atomized fluid. The chamber inlet houses a multi-jet nozzle for fluid mixing, which is followed by a nozzle for an optional introduction of the additional reagents. The working chamber has a circular threshold-shaped runner attached to its interior. The inner surface of the chamber's back comprises the radial longitudinal ribs. It should be noted, that the device is not capable of generating uniform cavitation field within the chamber, and, as a result, the efficiency of processing is insufficient.
In the present time, with the cost of energy rapidly rising, it is highly desirable to reduce time and lower energy consumption to secure a profit margin that is as large as possible. However, prior art techniques do not offer the most efficient method of blending and upgrading fluids, especially complex mixtures and non-Newtonian viscous liquids, in the shortest amount of time possible.
Thus, a need exists in an advanced flow-through device for the complex fluid processing with a minimal time treatment and energy cost that would result in products with improved characteristics that would be easier to handle. The advanced, compact, and highly efficient device is particularly needed at the mining locations and refineries, where throughput is a key factor. Several other objects and advantages of the present invention are:                (1) to provide a flow-through hydrodynamic multi-stage cavitation device for processing fluids in a an expedited manner with the optimized energy costs;        (2) to make easier operation, improve productivity and reduce room taken up by the processing equipment;        (3) to provide conditions for mixing and altering fluids by passing them through the cavitation vortices and bubbles generation zones as well as working chambers with the high fluid pressure for the cavitation bubbles' implosion at the gradually increasing temperature, decreasing the cavitation thresholds;        (4) to provide conditions for the gradual, cascade, multi-step alteration of fluids by subjecting the original constituents of the said fluids to the first cavitation event followed by subjecting the residual original compounds and products of the reactions to the second cavitation event, and etc.        (5) to provide a device for manipulating fluids at the site of their production;        (6) to provide conditions to obtain changes in crude oil resembling those of thermo cracking;        
(7) to produce even cavitation field throughout the volume and for time sufficient for synthesizing new stable molecules and producing other changes;                (8) to provide the device, wherein two or more a flow-through hydrodynamic multi-stage cavitation systems can be employed.        
The present invention fulfills these needs and provides other related advantages.